Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing a new design according to a first embodiment; and,

FIG. 2 is a front view of the display screen or portion thereof with a graphical user interface showing the new design according to a second embodiment.

Within the drawings, the outermost dashed broken-line perimeter illustrates a display screen or portion thereof and forms no part of the claimed design. The remaining dashed broken lines illustrate portions of a graphical user interface and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 